The construction of swirl pressure nozzles is well known. They have a nozzle body, in which typically a conical tapered inner area is provided. One or more inlets lead into this tapered inner area in an essentially tangential manner, more precisely to the end section of the tapered inner area with the largest diameter. At the end of the inner area with the smallest diameter, the inner area leads into the outlet of the nozzle.
In operation a fluid medium is fed under pressure through the inlet in an essentially tangential manner into the tapered inner area, more precisely into the end section of the inner area with the largest diameter. The fed fluid medium moves along the inner wall, which forms the tapered inner area, and forms there a fluid film when the ratio of tangential to axial speed is sufficient. If the fluid medium reaches the end of the inner area with the smallest diameter—therefore the section where the tapered inner area joins the outlet of the nozzle—and if the fluid medium goes through the outlet, the film breaks away and it forms fine droplets outside the outlet of the nozzle.
Such nozzles are employed for example in energy generation processes which use gas turbines. The air flow volume sucked in by the compressor has a variable density according to climatic conditions. The customary performance indication of gas turbines is based on ISO-standard values (at 15° C., 60% relative humidity, 1013 hPa pressure). If the air temperature rises, the density of the incoming air decreases, and so a decrease of the performance of the gas turbine will be noted. With the help of nozzles, fine water droplets can be added to the incoming air, in which a decrease of the air temperature is brought about by evaporation and therefore an increase in the density occurs. The consequence is that the performance of the gas turbine improves.
In principle it is possible to vaporise so many water droplets in the air current (“fogging”), until the relative humidity is 100%. As a result the aforementioned cooling of the air occurs, and the air density is increased. However if the air is completely saturated, droplets can no longer be vaporised with an additional influx of water droplets.
Nevertheless, it is known that a further influx of water droplets (“overfogging”) can have the consequence that the amount of electrical energy which is extractable from the turbine increases, even though the water droplets can no longer be vaporised in the air current in the air admission channel. That nevertheless the amount of extractable electrical energy increases, is a result of the fact that by supply of the air current to the turbine, the air in the compressor sector of the turbine is compressed, which warms up the previously saturated air and thus making it able to take up additional moisture. The surplus water droplets contained in the air current in the air admission channel can then be vaporised by the elevated temperature in the air current and can contribute to the increase of the electrical energy which is extractable from the turbine.
As a result of the supply of such an air current oversaturated with water droplets, there is the danger that erosion in the compressor section of the gas turbine can occur. So that such an erosion does not occur, the droplet sizes of the water drops are not allowed to be greater than about 10–30 μm. However, the generation of such fine droplets is not so trivial and places high demands on the corresponding nozzles with which such fine droplets are to be produced.
A known type of nozzle with which it is possible to produce such fine water droplets, is the so called “rebound bow nozzle” (“Prallbügel-Düse”). Such a rebound bow nozzle has a bent bow—the rebound bow—whose peak is arranged opposite the outlet of the nozzle. The water jet coming out of the outlet of the nozzle collides against the peak of this rebound bow, which results in a spray being formed and the desired fine water droplets being created.
This nozzle per se is in working order. However the rebound bow must be adjusted very exactly relative to the outlet, so that the desired fine droplets can be formed. This exact adjustment of the rebound bow relative to the outlet must always be maintained, in which it must be taken into account that the rebound bow is extremely exposed both during installation as well as during operation. In addition, the production of the nozzle is difficult, and also it has disadvantages with regard to its service life. Also with a rebound bow nozzle erosion can appear with time, so that from time to time the nozzle must be changed to ensure that the desired spray quality (maximal droplet size) can be guaranteed. This considerably reduces the profitability of the nozzle itself and also of the total facility, because the change of the nozzles can not be effected without an interruption of the system.
Although in principle the swirl pressure nozzles described in the beginning function very reliably and also have a very good service life, hitherto they have not been able to be employed for such a use, because with this type of nozzle the finest required droplets could not be produced.